初学Java，编写的一段小程序，运行结果有点问题，检查多时未果，求大家指导？

Question

是用来统计出现的词语的数量的程序，第一个文件是一些要统计的词语，第二个是一个空文件，暂时没啥用。
import java.io.*;
import java.util.*;
public class cotest {
public static void main(String args[]){
File readFile=new File("F:/code/coword.txt"),
writeFile= new File("F:/code/hello.txt");
try{
FileReader inOne=new FileReader(readFile);
BufferedReader inTwo=new BufferedReader(inOne);
FileWriter tofile=new FileWriter("hello.txt");
BufferedWriter out=new BufferedWriter(tofile);
String s=null;
int n;
String a=new String();
str_nu new_word=new str_nu();
LinkedList words=new LinkedList();
while((s=inTwo.readLine())!=null){
Scanner sc=new Scanner(s);
while(sc.hasNext()){
a=sc.next();
//System.out.println(a);
n=getIndex(words,a);

                    //System.out.println(n);
                    if(n!=-1){
                        words.get(n).num++;
                        System.out.println(words.get(n).num);
                    }
                    else{
                        new_word.word=a;
                        new_word.num=1;
                        words.add(new_word);
                    }


            }
        }
        for(int i=0;i<words.size();i++){
            System.out.println("单词："+words.get(i).word+" "+words.get(i).num);
            if(words.get(i).word=="ccc")
                System.out.println("here");
        }
        if(words.get(1).word=="ccc")
            System.out.println("abcd");

        inOne.close();
        inTwo.close();
    }
    catch(IOException e){
        System.out.println(e);
    }

}

private static int getIndex(LinkedList<str_nu> words, String a) {
    // TODO Auto-generated method stub
    for(int i=0;i<words.size();i++){
        if(words.get(i).word==a){
            System.out.println(i);
            return i;

        }
    }

    return -1;
}

}

class str_nu{
String word=new String();
int num;
}

Answer 1

字符串精确比较要使用String类的equals方法，不能使用 ==

if(words.get(i).word=="ccc")
if(words.get(i).word==a){